Method for determining the desired decoupling components for power distribution systems

ABSTRACT

A method for determining the desired decoupling components for stabilizing the electrical impedance in the power distribution system of an electrical interconnecting apparatus, including a method for measuring the ESR for an electrical device, a method for determining a number of desired decoupling components for a power distribution system, and a method for placing the desired decoupling components in the power distribution system. The method creates a model of the power distribution system based upon an M×N grid for both the power plane and the ground plane. The model receives input from a user and from a database of various characteristics for a plurality of decoupling components. The method determines a target impedance over a desired frequency range. The method selects decoupling components. The method determines a number for each of the decoupling components chosen. The method places current sources in the model at spatial locations corresponding to physical locations of active components. The method optionally also places a power supply in the model. The method selects specific locations in the model to calculate transfer impedance values as a function of frequency. The method effectuates the model to determine the transfer impedance values as the function of frequency at the specific locations previously chosen. The method then compares the transfer impedance values as the function of frequency at the specific locations to the target impedance for the power distribution system. The method determines a bill of goods for the power distribution system based upon the results of effectuating the model.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to electronic systems, and more particularly toelectrical interconnecting apparatus having continuous planarconductors.

2. Description of the Related Art

Electronic systems typically employ several different types ofelectrical interconnecting apparatus having planar layers ofelectrically conductive material (i.e., planar conductors) separated bydielectric layers. A portion of the conductive layers may be patternedto form electrically conductive signal lines or “traces”. Conductivetraces in different layers (i.e., on different levels) are typicallyconnected using contact structures formed in openings in the dielectriclayers (i.e., vias). For example, integrated circuits typically haveseveral layers of conductive traces which interconnect electronicdevices formed upon and within a semiconductor substrate. Each layer isseparated from adjacent layers by dielectric layers. Within asemiconductor device package, several layers of conductive tracesseparated by dielectric layers may be used to electrically connectbonding pads of an integrated circuit to terminals (e.g., pins or leads)of the device package. Printed circuit boards (PCBs) also typically haveseveral layers of conductive traces separated by dielectric layers. Theconductive traces are used to electrically interconnect terminals ofelectronic devices mounted upon the PCB.

Signals in digital electronic systems typically carry information byalternating between two voltage levels (i.e., a low voltage level and ahigh voltage level). A digital signal cannot transition instantaneouslyfrom the low voltage level to the high voltage level, or vice versa. Thefinite amount of time during which a digital signal transitions from thelow voltage level to the high voltage level is called the rise time ofthe signal. Similarly, the finite amount of time during which a digitalsignal transitions from the high voltage level to the low voltage levelis called the fall time of the signal.

Digital electronic systems are continually being produced which operateat higher signal frequencies (i.e., higher speeds). In order for thedigital signals within such systems to remain stable for appreciableperiods of time between transitions, the rise and fall times of thesignals must decrease as signal frequencies increase. This decrease insignal transition times (i.e., rise and fall times) creates severalproblems within digital electronic systems, including signal degradationdue to reflections, power supply “droop”, ground “bounce”, and increasedelectromagnetic emissions. It is desirable that the digital signals aretransmitted and received within accepted tolerances.

A signal launched from a source end of a conductive trace suffersdegradation when a portion of the signal reflected from a load end ofthe trace arrives at the source end after the transition is complete(i.e., after the rise time or fall time of the signal). A portion of thesignal is reflected back from the load end of the trace when the inputimpedance of the load does not match the characteristic impedance of thetrace. When the length of a conductive trace is greater than the risetime divided by three, the effects of reflections upon signal integrity(i.e., transmission line effects) should be considered. If necessary,steps should be taken to minimize the degradations of signals conveyedupon the trace due to reflections. The act of altering impedances at thesource or load ends of the trace in order to reduce signal reflectionsis referred to as “terminating” the trace. For example, the inputimpedance of the load may be altered to match the characteristicimpedance of the trace in order to prevent signal reflection. As thetransition time (i.e., the rise or fall time) of the signal decreases,so does the length of trace which must be terminated in order to reducesignal degradation.

A digital signal alternating between the high and low voltage levelsincludes contributions from a fundamental sinusoidal frequency (i.e., afirst harmonic) and integer multiples of the first harmonic. As the riseand fall times of a digital signal decrease, the magnitudes of a greaternumber of the integer multiples of the first harmonic becomesignificant. As a general rule, the frequency content of a digitalsignal extends to a frequency equal to the reciprocal of π times thetransition time (i.e., rise or fall time) of the signal. For example, adigital signal with a 1 nanosecond transition time has a frequencycontent extending up to about 318 MHz.

All conductors have a certain amount of inductance. The voltage acrossthe inductance of a conductor is directly proportional to the rate ofchange of current through the conductor. At the high frequencies presentin conductors carrying digital signals having short transition times, asignificant voltage drop occurs across a conductor having even a smallinductance. A power supply conductor connects one terminal of anelectrical power supply to a power supply terminal of a device, and aground conductor connects a ground terminal of the power supply to aground terminal of the device. When the device generates a digitalsignal having short transition times, high frequency transient loadcurrents flow in the power supply and ground conductors. Power supplydroop is the term used to describe the decrease in voltage at the powersupply terminal of the device due to the flow of transient load currentthrough the inductance of the power supply conductor. Similarly, groundbounce is the term used to describe the increase in voltage at theground terminal of the device due to the flow of transient load currentthrough the inductance of the ground conductor. When the devicegenerates several digital signals having short transition timessimultaneously, the power supply droop and ground bounce effects areadditive. Sufficient power supply droop and ground bounce can cause thedevice to fail to function correctly.

Power supply droop is commonly reduced by arranging power supplyconductors to form a crisscross network of intersecting power supplyconductors (i.e., a power supply grid). Such a grid network has a lowerinductance, hence power supply droop is reduced. A continuous powersupply plane may also be provided which has an even lower inductancethan a grid network. Placing a “bypass” capacitor near the power supplyterminal of the device is also used to reduce power supply droop. Thebypass capacitor supplies a substantial amount of the transient loadcurrent, thereby reducing the amount of transient load current flowingthrough the power supply conductor. Ground bounce is reduced by using alow inductance ground conductor grid network, or a continuous groundplane having an even lower amount of inductance. Power supply and groundgrids or planes are commonly placed in close proximity to one another inorder to further reduce the inductances of the grids or planes.

Electromagnetic interference (EMI) is the term used to describe unwantedinterference energies either conducted as currents or radiated aselectromagnetic fields. High frequency components present withincircuits producing digital signals having short transition times may becoupled into nearby electronic systems (e.g., radio and televisioncircuits), disrupting proper operation of these systems. The UnitedStates Federal Communication Commission has established upper limits forthe amounts of EMI products for sale in the United States may generate.

Signal circuits form current loops which radiate magnetic fields in adifferential mode. Differential mode EMI is usually reduced by reducingthe areas proscribed by the circuits and the magnitudes of the signalcurrents. Impedances of power and ground conductors create voltage dropsalong the conductors, causing the conductors to radiate electric fieldsin a common mode. Common mode EMI is typically reduced by reducing theimpedances of the power and ground conductors. Reducing the impedancesof the power and ground conductors thus reduces EMI as well as powersupply droop and ground bounce.

Within the wide frequency range present within electronic systems withdigital signals having short transition times, the electrical impedancebetween any two parallel conductive planes (e.g., adjacent power andground planes) may vary widely. The parallel conductive planes mayexhibit multiple electrical resonances, resulting in alternating highand low impedance values. Parallel conductive planes tend to radiate asignificant amount of differential mode EMI at their boundaries (i.e.,from their edges). The magnitude of differential mode EMI radiated fromthe edges of the parallel conductive planes varies with frequency and isdirectly proportional to the electrical impedance between the planes.

FIG. 1 is a perspective view of a pair of 10 in.×10 in. squareconductive planes 110 and 120 separated by a fiberglass-epoxy compositedielectric layer. Each conductive plane is made of copper and is 0.0014in. thick. The fiberglass-epoxy composite layer separating the planeshas a dielectric constant of 4.0 and is 0.004 in. thick. If a 1 ampereconstant current is supplied between the centers of the rectangularplanes, with a varying frequency of the current, the magnitude of thesteady state voltage between the centers of the rectangular planes canbe determined 130.

The electrical impedance between the parallel conductive planes of FIG.1 varies widely at frequencies above about 200 MHz. The parallelconductive planes exhibit multiple electrical resonances at frequenciesbetween 100 MHz and 1 GHz and above, resulting in alternating high andlow impedance values. The parallel conductive planes of FIG. 1 wouldalso radiate substantial amounts of EMI at frequencies where theelectrical impedance between the planes anywhere near their peripheriesis high.

The above problems are currently solved in different ways at differentfrequency ranges. At low frequency, the power supply uses a negativefeedback loop to reduce fluctuations. At higher frequencies, large valuebypass (i.e. decoupling) capacitors are placed near devices. At thehighest frequencies, up to about 200-300 MHz, very small bypasscapacitors are placed very close to devices in an attempt to reducetheir parasitic inductance, and thus high frequency impedance, to aminimum value. By Nov. 2, 1994, the practical upper limit remainedaround 200-300 MHz as shown by Smith [Decoupling Capacitor Calculationsfor CMOS Circuits; pp. 101-105 in Proceedings of 3^(rd) Topical Meetingon Electrical Performance of Electronic Packaging of the Institute ofElectrical and Electronics Engineers, Inc.].

The power distribution system was modeled as shown in FIG. 2. Aswitching power supply 210 supplies current and voltage to a CMOS chipload 220. In parallel with the power supply 210 and the load 220 aredecoupling capacitors 215 and the PCB 225 itself, with its owncapacitance. Smith [1994] teaches that decoupling capacitors are onlynecessary up to 200-300 MHz, as the target impedances are rarelyexceeded above that frequency. This upper limit changes over time as theclock frequencies increase and the allowable voltage ripple decreases.Determining the proper values for decoupling capacitors and the optimumnumber of each has been a “trial and error” process, which relies on theexperience of the designer. There are no known straightforward rules forchoosing decoupling capacitors for all frequency ranges.

It would thus be desirable to have a method for designing the powerdistribution system and determining the desired decoupling componentsfor stabilizing the electrical impedance in the power distributionsystem. The method is preferably automatable using a computer system toperform calculations.

SUMMARY OF THE INVENTION

The problems outlined above are in large part solved by a method fordetermining the desired decoupling components for stabilizing theelectrical impedance in the power distribution system of an electricalinterconnecting apparatus including a pair of parallel planar conductorsseparated by a dielectric layer. The electrical interconnectingapparatus may be, for example, a PCB, a semiconductor device packagesubstrate, or an integrated circuit substrate. The present methodincludes creating a model of the power distribution system based upon anM×N grid for both the power plane and the ground plane. The model ispreferably based upon a fixed grid which adapts automatically to theactual physical dimensions of the electrical interconnecting apparatus.The model preferably also calculates the system response to chosendecoupling components in both single node and M×N node versions.

The model receives input from a user and from a database of variousphysical and/or electrical characteristics for a plurality of decouplingcomponents. Various characteristics of interest include physicaldimensions, type and thickness of dielectric, method and materials ofmanufacture, capacitance, mounted inductance, and ESR. The desiredcharacteristics are preferably saved in a database for corrections,additions, deletions, and updates.

In one embodiment, the model of the power distribution system is in aform of a plane including two dimensional distributed transmissionlines. The model of the power distribution system may comprise aplurality of the following: one or more physical dimensions of the powerplane, one or more physical dimensions of the ground plane, physicalseparation distance of the power plane and the ground plane, compositionof a dielectric separating the power plane and the ground plane, one ormore active device characteristics, one or more power supplycharacteristics, and one or more of the decoupling components. In oneembodiment, M and N have a uniform value. In various embodiments, theactive components act as current sources or sinks, and may includeprocessors, memories, application specific integrated circuits (ASICs),logic ICs, or any device which converts electrical energy intoinformation. Preferably, a total sum of all values of the currentsources in the model is scaled to equal one ampere.

In one embodiment, the model of the power distribution system isoperable for determining the decoupling components for a frequency rangeabove approximately a lowest board resonance frequency. In anotherembodiment, the model of the power distribution system is operable fordetermining the decoupling components for a frequency range above ahighest resonance frequency from all resonance frequencies of thedecoupling components.

The method preferably includes determining a target impedance for thepower distribution system at a desired frequency or over a desiredfrequency range. The target impedance is preferably determined basedupon such factors as power supply voltage, total current consumption,and allowable voltage ripple in the power distribution system.Preferably, determining the target impedance for the power distributionsystem comprises the quotient of power supply voltage multiplied byallowable voltage ripple divided by total current.

The frequency range may start at dc and rise to several GHz. In oneembodiment, the model of the power distribution system is operable fordetermining the decoupling components for a frequency range aboveapproximately a lowest board resonance frequency. In another embodiment,the model of the power distribution system is operable for determiningthe decoupling components for a frequency range above a highestresonance frequency from all resonance frequencies of the decouplingcomponents.

The method preferably selects one or more decoupling components from aplurality of possible decoupling components. Preferably, the decouplingcomponents are capacitors with an approximate mounted inductance and anESR. In one embodiment, a range of the values of the capacitors ischosen such that a superposition of impedance profiles provide animpedance at or below the target impedance for the power distributionsystem over the frequency range of interest. In one embodiment, theimpedance profiles of the plurality of possible decoupling componentsare compared to resonance frequencies for the power distribution system.The decoupling components have resonance frequencies which substantiallycorrespond to the resonance frequencies of the power distribution systemin the frequency range of interest.

The method preferably determines a number for each of the one or moredecoupling components chosen to be included as part of the powerdistribution model. In one embodiment, the number of the variousdecoupling components is chosen based upon the frequency range ofinterest and the impedance profiles of a plurality of possibledecoupling components. In another embodiment, the number of a particularone of the decoupling components is chosen to have approximately equalvalue of a next larger integer of the quotient obtained from dividingthe ESR for the particular decoupling components by the target impedancefor the power distribution system. In still another embodiment, thenumber of particular decoupling components has approximately equal valueof impedance to the target impedance for the power distribution systemwhen the number of the particular decoupling components are placed inparallel. In one embodiment, determining the number for the each of thedecoupling components occurs before effectuating the model of the powerdistribution system to determine the transfer impedance values as thefunction of frequency at the one or more specific locations.

The method preferably places one or more current sources in the model ofthe power distribution system at one or more spatial locationscorresponding to one or more locations of active components. The methodalso preferably places the decoupling components in the model of thepower distribution system at nodal points that couple the M×N grid forthe power plane and the corresponding M×N grid for the ground plane. Inone embodiment, the method places a power supply in the model of thepower distribution system at a fixed location on the power plane. Thepower supply is preferably comprised in the model as one or more polefrequencies, one or more zero frequencies, and one or more resistances.

The method preferably selects one or more specific locations in themodel of the power distribution system to calculate transfer impedancevalues as a function of frequency. The method preferably effectuates themodel of the power distribution system to determine the transferimpedance values as the function of frequency at the one or morespecific locations previously chosen. The method then preferablycompares the transfer impedance values as the function of frequency atthe one or more specific locations to the target impedance for the powerdistribution system. Preferably, the method determines a bill of goodsfor the power distribution system based upon the results of effectuatingthe model.

In various embodiments, the method for determining decoupling componentsfor a power distribution system includes determining a preferred oroptimum number of decoupling components for a power distribution system.A preferred method for determining a number of decoupling components fora power distribution system is also disclosed. For a given frequency orfrequency range, the method for determining a number of decouplingcomponents for a power distribution system comprises selecting aparticular one of the decoupling components based upon a mountedinductance of each of the decoupling components. The mounted inductancecomprises an indication of a resonance frequency of that particular oneof the decoupling components. The method also compares an individualdecoupling component impedance of each of the decoupling components tothe target impedance. The method then selects the number of theparticular one of the decoupling components which provides a totalimpedance at or below the target impedance at the given frequency orfrequency range.

In one embodiment, if the impedance of the particular decouplingcomponent is greater than the target impedance, then the methodcalculates the desired number of the particular decoupling components ina parallel configuration. In embodiments that determine a number of eachof a plurality of decoupling components for a power distribution systemfor a given frequency range, a plurality of decoupling components arechosen as necessary to provide a total impedance at or below the targetimpedance for the given frequency range.

In various embodiments, the method for determining decoupling componentsfor a power distribution system includes determining placementinformation for preferred or optimum number of decoupling components fora power distribution system. A preferred method for determiningplacement of one or more decoupling components in a power distributionsystem is also given. In one embodiment, each of the one or moredecoupling components includes a respective resonance frequency and arespective equivalent series resistance at the respective resonancefrequency. The power distribution system includes a target impedance,and the electrical interconnecting apparatus has at least a firstdimension. The method determines one or more board resonancefrequencies. A first board frequency corresponds to the first dimension.The method also selects one or more first decoupling components from aplurality of possible decoupling components such that the firstdecoupling components have their respective resonance frequency atapproximately the first board resonance frequency. The method thenplaces the first decoupling components on a location of the electricalinterconnecting apparatus corresponding to the first dimension.Additional dimensions of the electrical interconnecting apparatus mayalso require their own decoupling components.

In the embodiment where the electrical interconnecting apparatus hasapproximately rectangular dimensions, the first dimension is preferablyan effective length and the second dimension is preferably an effectivewidth. The preferred location for placing the decoupling component forthe first dimension comprises a first edge on the effective length,while the preferred location for placing the decoupling component forthe second dimension comprises a second edge on the effective width.

In one embodiment, when the electrical interconnecting apparatus has atleast one location for at least a first active device, the methodfurther comprises placing one or more second decoupling components onthe electrical interconnecting apparatus at the at least one locationfor at least the first active device. Additional decoupling componentsare also placed on the electrical interconnecting apparatus as neededfor additional active devices. The preferred location for placingdecoupling components for active devices is at or near the activedevices.

In one embodiment, the method includes selecting the decouplingcomponents from a plurality of possible decoupling components such thatthe decoupling components have the respective resonance frequency atapproximately the first operating frequency of the active device.Additional decoupling components may be selected and placed based uponthe harmonics of the operating frequency, as desired.

BRIEF DESCRIPTION OF THE DRAWINGS

Other objects and advantages of the invention will become apparent uponreading the following detailed description and upon reference to theaccompanying drawings in which:

FIG. 1 is a perspective view of a representative electricalinterconnecting apparatus comprising a prior art pair of 10 in.×10 in.square conductive planes separated by a fiberglass-epoxy compositedielectric layer;

FIG. 2 is an embodiment of a prior art single node model of a powerdistribution system;

FIG. 3A is a top view of one embodiment of a model of a powerdistribution system;

FIG. 3B is an embodiment of a unit cell of the power distribution systemmodel shown in FIG. 3A;

FIG. 4 is a representative grid of the nodal interconnections of themodel of the power distribution system shown in FIG. 3A;

FIG. 5 is a flowchart of an embodiment of a method for determiningdecoupling components for a power distribution system;

FIG. 6 is a flowchart of an embodiment of a method for measuring theequivalent series resistance of an electrical device;

FIG. 7 is a flowchart of an embodiment of a method for placingdecoupling components in a power distribution system;

FIG. 8A is a block diagram of an embodiment of a computer systemoperable to implement the methods of determining the decouplingcomponents for a power distribution system;

FIG. 8B is a flowchart of an embodiment of the method for determiningdecoupling components for a power distribution system using the computersystem of FIG. 8A; and

FIG. 9 is a flowchart of another embodiment of the method fordetermining decoupling components for a power distribution system usingthe computer system of FIG. 8A.

While the invention is susceptible to various modifications andalternative forms, specific embodiments thereof are shown by way ofexample in the drawings and will herein be described in detail. Itshould be understood, however, that the drawings and detaileddescription thereto are not intended to limit the invention to theparticular form disclosed, but on the contrary, the intention is tocover all modifications, equivalents and alternatives falling within thespirit and scope of the present invention as defined by the appendedclaims.

DETAILED DESCRIPTION OF THE INVENTION

Incorporation by Reference

The following publications are hereby incorporated by reference in theirentirety:

“Decoupling Capacitor Calculations for CMOS Circuits” by Larry D. Smith,IEEE Proceedings of the 3^(rd) Topical. Meeting on ElectricalPerformance of Electronic Packaging, Nov. 2, 1994, and

“Packaging and Power Distribution Design Considerations for a SunMicrosystems Desktop Workstation” by Larry D. Smith, IEEE Proceedings ofthe 6^(th) Topical Meeting on Electrical Performance of ElectronicPackaging, Oct. 27, 1997.

FIG. 3—Power Distribution System Model

FIG. 3A is a top view of a simplified schematic of one embodiment of amodel of a power distribution system. As shown, the model comprises agrid 300A of transmission line segments. The segments are grouped intounit cells 350. As shown, there are eight columns labeled “a” through“h”, as well as eight rows labeled, from the bottom to the top, “1”through “8”. The model preferably comprises a SPICE array oftransmission lines in a fixed topology (i.e. in an 8×8 grid). Thetransmission lines are variable lengths such that the fixed topology maybe used on electrical connecting device of any physical dimensions. Itis noted that other embodiments of the power distribution system arecontemplated, such as an elliptical model based on a “wheel and spoke”geometry.

FIG. 3B illustrates a close up view of the unit cell 350 from FIG. 3A.As shown, the unit cell 350 is comprised of four transmission lines355A-355D. The four transmission lines 355 connect together at nodalpoint pair 370, also referred to as node 370. As shown, connections tothe center conductors represent plane 1, while connections to shield areplane 2. Note that the model is balanced, therefore either plane 1 orplane 2 may be power or ground, as desired. Transmission lines 355A and355B are preferably described with a width impedance “Z_(W)” and a widthtime delay “t_(DW)”. Transmission lines 355C and 355D are preferablydescribed with a length impedance “Z_(L)” and a length time delay“t_(DL)”. R₁ and R₂ are resistances. The constants, parameters andvariables of interest, as well as the equations that define and relatethese quantities, along with the preferred units are given below:

“L” is the length of the plane (inches)

“W” is the width of the plane (inches)

“thk” is the thickness of the dielectric (mils)

“cu” is the metalization thickness (mils)

“velc” is the speed of light in a vacuum (inches/sec)

“hertz” is the frequency variable

“∈₀” is the vacuum dielectric constant (permittivity) (picofarads/inch)

“∈_(r)” is the dielectric constant

“σ” is the copper conductivity (per ohm/mils)

“μ₀” is the permeability of a vacuum (henries/mil)

“vel” is the velocity of a signal on the electrical interconnectingapparatus

vel=velc/{square root over (∈_(r))}

“n” is the size of the grid, i.e. 8 as shown

“asp” is the aspect ratio of the grid, asp=L/W

“factor” is a calibration factor to compensate for capacitive loading

factor=1/{square root over (2)}

“t_(FL)” is the time of flight for the length dimension, t_(FL)=L/vel

“t_(FW)” is the time of flight for the width dimension, t_(FW)=W/vel

“t_(DL)” is the transmission line delay time for the length dimension

t _(DL) =t _(FL)/(2n)factor

“t_(DW)” is the transmission line delay time for the width dimension

t _(DW) =t _(FW)/(2n)factor

“cap” is the parallel plate capacitance of the plane

cap=(∈₀∈_(r) LW)/(10⁻⁹ thk)

“Z_(L)” is the impedance in the length direction

Z _(L)=(n/cap)(t _(FL) +asp*t _(FW))factor

“Z_(W)” is the impedance in the width direction, Z_(W)=Z_(L)/asp

“R₁” is the smaller of:

R _(1A)=((L/W)/2)*(1/(σ*(1/{square root over (hertz*πμ₀σ)})))

R _(1B)=((L/W)/2)*(1/(σ*cu))

“R₂” is the smaller of:

R _(2A)=((W/L)/2)*(1/(σ*(1/{square root over (hertz*πμ₀σ)})))

R _(2B)=((W/L)/2)*(1/(σ*cu))

The model represents an electrical interconnecting apparatus, which maybe, for example, a printed circuit board (PCB), a semiconductor devicepackage substrate, or an integrated circuit substrate. The presentmethod includes creating a model of the power distribution system basedupon an M×N grid for both the power plane and the ground plane. Themodel is preferably based upon a fixed grid that adapts automatically tothe actual physical dimensions of the electrical interconnectingapparatus. The model preferably also calculates the system response tochosen decoupling components in both single node and M×N node versions.

The model receives input from a user and from a database of variousphysical and/or electrical characteristics for a plurality of decouplingcomponents. Various characteristics of interest include physicaldimensions, type and thickness of dielectric, method and materials ofmanufacture, capacitance, mounted inductance, and equivalent seriesresistance (ESR). The desired characteristics are preferably saved in adatabase for corrections, additions, deletions, and updates.

In one embodiment, the model of the power distribution system is in aform of a plane including two dimensional distributed transmissionlines. The model of the power distribution system may comprise aplurality of the following: one or more physical dimensions of the powerplane, one or more physical dimensions of the ground plane, physicalseparation distance of the power plane and the ground plane, compositionof a dielectric separating the power plane and the ground plane, one ormore active device characteristics, one or more power supplycharacteristics, and one or more of the decoupling components. In apreferred embodiment, M and N have a uniform value, 8 as shown. Invarious embodiments, the active components act as current sources orsinks, and may include processors, memories, application specificintegrated circuits (ASICs), or logic ICs. Preferably, a total sum ofall values of the current sources in the model is scaled to equal oneampere.

In one embodiment, the model of the power distribution system isoperable for determining the decoupling components for a frequency rangeabove approximately a lowest board resonance frequency. Additionalinformation on board resonance frequencies is found later with respectto FIG. 5. In another embodiment, the model of the power distributionsystem is operable for determining the decoupling components for afrequency range above a highest resonance frequency from all resonancefrequencies of the decoupling components.

In one embodiment, the model uses a weighting factor in determining anumber of a particular decoupling component to include in the model. Theweighting factor is a dimensionless non-zero positive number. In thefrequency range where EMI is most important, the preferred weightingfactor is 0.2. The EMI frequency range is preferably above approximately200 MHz. Preferably, the weighting factor is 1.0 in a frequency rangewhere signal integrity is most important. The frequency range wheresignal integrity is important is preferably approximately 10 MHz up toapproximately 200-300 MHz. The weighting factor is preferably 2.0 at allactive device operating frequencies and harmonics of the active deviceoperating frequencies. In a preferred embodiment, the model includes afrequency dependent skin effect loss.

FIG. 4—Grid

FIG. 4 illustrates the 8×8 grid 300B of nodes 370 that are used to modelthe power and ground planes with the respective designations of a1through h8, in a preferred embodiment. This grid 300B is used todetermine the locations of the decoupling components for the powerdistribution system.

FIG. 5—Method for Determining Decoupling Components

FIG. 5 illustrates a flowchart of an embodiment of a method fordetermining decoupling components for a power distribution system. Themethod is shown as a straight through method with no loop-back. In otherembodiments, the method includes feedback loops at various stages tochange previous inputs.

The method determines a target impedance for the power distributionsystem 510. The target impedance is preferably determined at a desiredfrequency or over a desired frequency range. The target impedance isdetermined based upon such factors as power supply voltage, totalcurrent consumption, and allowable voltage ripple in the powerdistribution system. Preferably, determining the target impedance forthe power distribution system comprises the quotient of power supplyvoltage multiplied by allowable voltage ripple divided by total current.In a preferred embodiment, the total current is normalized to oneampere. The target impedance may be comprised in a group of known systemparameters. Other known system parameters may include one or more powersupply characteristics, the allowable voltage ripple, the total currentconsumption of all devices, one or more physical dimensions of the powerdistribution system, physical location constraints on where devices maybe placed in the power distribution system, and/or a frequency orfrequency range of interest.

The method preferably selects a frequency range of interest 515. Thefrequency range may start at dc and rise up to or above the gigahertzrange. In one embodiment, the model of the power distribution system isoperable for determining the decoupling components for a frequency rangeabove approximately a lowest board resonance frequency. In anotherembodiment, the model of the power distribution system is operable fordetermining the decoupling components for a frequency range above ahighest resonance frequency from all resonance frequencies of thedecoupling components. As mentioned above, the frequency range ofinterest may be comprised in the known system parameters. In oneembodiment, the frequency range of interest determines the output of themethod by limiting the frequency range over which the system impedanceis calculated in the model.

The method preferably determines the ESR for the plurality of decouplingcomponents 520. The decoupling components are preferably capacitors, butother devices with desirable capacitive and inductive values may beused. The ESR is preferably included in the database of various physicaland/or electrical characteristics for the plurality of decouplingcomponents. Various other characteristics of interest may includephysical dimensions, type and thickness of dielectric, method andmaterials of manufacture, capacitance, and mounted inductance. Thedesired characteristics are preferably saved in the database forcorrections, additions, deletions, and updates.

Additional details concerning determining the ESR for the plurality ofdecoupling components 520 is given below with respect to FIG. 6.

The method preferably selects one or more desirable decouplingcomponents from a plurality of possible decoupling components 525.Preferably, the decoupling components are capacitors with an approximatemounted inductance and an ESR. In one embodiment, a range of the valuesof the capacitors is chosen such that a superposition of impedanceprofiles provide an impedance at or below the target impedance for thepower distribution system over the frequency range of interest. Inanother embodiment, the impedance profiles of the plurality of possibledecoupling components are compared to resonance frequencies for thepower distribution system.

The decoupling components have resonance frequencies, which shouldsubstantially correspond to the resonance frequencies of the powerdistribution system in the frequency range of interest. Resonancefrequencies for the decoupling components are preferably chosen toapproximately correspond to board resonance frequencies, operatingfrequencies and harmonics of active devices, including power supply, onthe electrical interconnecting apparatus, and interaction resonancefrequencies, high frequency response frequencies from interactions ofthe various components in the power distribution system. In variousembodiments, the capacitors are selected by the type of manufacture,such as the dielectric composition, or a physical or electricalcharacteristic value, such as the mounted inductance. The mountedinductance includes the geometry and physical coupling to the electricalinterconnecting apparatus. The resonance frequency for a capacitor maybe calculated from the mounted inductance and the capacitance using thefollowing formula:

f _(resonance)=1/(2π{square root over (LC)})

The impedance of the capacitor at the resonance frequency is the ESR. Itis noted that ceramic capacitors often have a deep cusp at the resonancefrequency. Tantalum capacitors often have a deep broad bottom with avariable slope as a function of frequency.

Once the desired decoupling components have been selected, the optimumor desired number of each of the particular ones of the decouplingcomponents are determined by the method 530. In one embodiment, thenumber of each of the particular ones of the decoupling components aredetermined by the method 530 in response to the method selecting one ormore desirable decoupling components from a plurality of possibledecoupling components 525.

The method, therefore, preferably determines a number (i.e. a countingnumber, 1, 2, . . . ) for each of the one or more decoupling componentschosen to be included as part of the power distribution model 530. Inother words, the method determines how many of each particulardecoupling component to include in the model. In one embodiment, thenumber of the various decoupling components is chosen based upon thefrequency range of interest and the impedance profiles of the pluralityof possible decoupling components. In another embodiment, the number ofa particular one of the decoupling components is chosen to haveapproximately equal value of a next larger integer of the quotientobtained from dividing the ESR for the particular decoupling componentsby the target impedance for the power distribution system.

In still another embodiment, the number of a particular decouplingcomponents has approximately equal value of impedance to the targetimpedance for the power distribution system when the number of theparticular decoupling components are placed in parallel. In oneembodiment, determining the number for the each of the decouplingcomponents 530 occurs before effectuating the model of the powerdistribution system to determine the transfer impedance values as thefunction of frequency at the one or more specific locations 560. Inanother embodiment, the number of a particular one of the one or moredecoupling components has approximately equal value of a next largerinteger of the quotient obtained from dividing an equivalent seriesresistance for the particular one of the one or more decouplingcomponents by the target impedance for the power distribution system. Instill another embodiment, the number of decoupling components isdetermined for all decoupling components 530 in the plurality ofpossible decoupling components (i.e. in the database described above)before selecting the decoupling components to be used in the model 525.The calculations for selecting decoupling components 525 and determiningthe number of each of the selected decoupling components 530 arepreferably performed by a computer system. Additional details may begleaned below with respect to FIGS. 7-9.

The method creates (i.e. realizes or implements) the model of the powerdistribution in 535. The preferred model is described above with respectto FIGS. 3A and 3B. In a preferred embodiment, the model iscomputerized. Additional details may be found elsewhere in thisdisclosure.

The method next populates the model of the power distribution system.That is, the method adds to the model those devices that are coupled tothe electrical interconnecting apparatus. The method places currentsources (or sinks) in the model at nodal points 370 on the M×N grid 300Bin 540. The current sources are placed at one or more spatial locationscorresponding to one or more locations of active-components. Examples ofactive components include processors, memories, application specificintegrated circuits (ASICs), or logic integrated circuits (logic ICs).It is noted that active devices may act as current sources or sinks. Thetotal value of the current sources is preferably scaled to one ampere.The numbers, current ratings and strengths, and locations of the currentsources may be included in the known system parameters. In oneembodiment, the placing of the current sources is performed by thecomputer system based on the known system parameters.

Optionally, the method places one or more power supplies in the modelplaced at nodal points 370 representing one or more spatial locations onthe electrical interconnecting apparatus 545. The power supply iscomprised in the model as one or more pole frequencies, one or more zerofrequencies, and one or more resistances. Preferably, one polefrequency, one zero frequency, and two resistances are used, along withthe output voltage. Typically, the parameters are treated as a serieswith one resistance in parallel with the, zero frequency. The parametersand locations of any power supplies are usually part of the known systemparameters. In one embodiment, placing the power supply in the model isperformed by the computer system. Additional details may be found withrespect to FIGS. 8-9.

The method also preferably places the decoupling components in the modelof the power distribution system at nodal points 370 that couple the M×Ngrid 300 for the power plane and the corresponding M×N grid for theground plane 550. Particular decoupling components should optimally beplaced as close as possible to those device locations which haveresonance frequencies in the frequency range of interest. Resonancefrequencies for the power distribution system should be interpreted inthis disclosure to include board resonance frequencies, operatingfrequencies and harmonics of active devices on the electricalinterconnecting apparatus, and high frequency response frequencies frominteractions of the various components in the power distribution system.High frequency response is often highly spatially dependent.

Board resonance frequencies are a function of the physical dimensions ofthe power distribution system and the dielectric constant of thedielectric that separates the power plane from the one or more groundplanes. The board resonance frequencies of interest in a preferredembodiment include the half-, full-, three-half-, second-full-, andfive-half-wave resonance frequencies for both the length and the width.The values for these board resonance frequencies are given by theappropriate multiples of vel, L, and W as defined earlier. For example,the half wave resonance for the length is (½)*vel*L. The three-half waveresonance for the width is ({fraction (3/2)})*vel*W.

To suppress the board resonance frequencies, decoupling components areplaced in the power distribution system at locations that provide a lowimpedance shunt for high impedance resonance nodes (i.e. high voltagestanding wave points). By noting where the board resonance has one ormore maximums, the placement follows at or near those correspondinglocations. For a half wave resonance, the decoupling components shouldbe placed along the edges of the power distribution system or theelectrical connecting apparatus. Since the apparatus is not onedimensional, the decoupling components are placed on the line resultingfrom the intersection of the resonance and the plane defining the powerdistribution system. Therefore, the decoupling components for the lengthhalf-wave resonance are preferably placed along the edges on the widthof the power distribution system. For the full wave resonance, thedecoupling components are preferably placed along the edges and alongthe center axis of the power distribution system. For thethree-half-wave resonance, the decoupling components are preferablyplaced along the edges and at points one-third in from each edge. Forthe second-full-wave resonance, the decoupling components are preferablyplaced along the edges, along the center axis, and at points one-fourthin from each edge. For the five-half-wave resonance, the decouplingcomponents are preferably placed along the edges, at points one-fifth infrom each edge, and at points two-fifths in from each edge. It is notedthat a square electrical connecting apparatus the lengthwise andwidthwise resonances will be at the same frequencies and have maximumsat corresponding locations. It is also noted that similar relations arefound with respect to an electrical connecting apparatus having adifferent geometry, such as elliptical, etc.

Resonance or operating frequencies for the power supply are usually lowenough that the capacitance can be treated as a lumped capacitance. Thusdecoupling components for the power supply may be placed anywhere on theelectrical interconnecting apparatus. Spatial limitations on locationsmust always be observed. This means that some decoupling components willbe placed farther away from the noise source than optimum. The modelwill often indicate that additional ones of those decoupling componentswill need to be placed on the electrical interconnecting apparatus atthe farther away location. In one embodiment, placement of decouplingcomponents 550 is input to the computerized model. Additional detailsmay be found in the descriptions of FIGS. 8-9.

The method preferably selects one or more specific locations in themodel of the power distribution system to calculate transfer impedancevalues 555 as a function of frequency. The specific locations preferablyinclude all 64 nodes on the 8×8 grid. To shorten execution time of thecomputer system, other numbers of nodes may be chosen. It is noted thatas the number of nodes increases, the model will accurately predict theboard resonance frequencies up to higher frequencies. In one embodiment,the model is run twice, once with a single specific node with allcomponents placed on the single specific node and then a second timewith the power distribution system filling the entire 64 nodes of themodel. The specific locations are usually part of the known systemparameters. It is noted that if fewer numbers of nodes are chosen, theusable bandwidth of the model will be lower.

The method preferably effectuates the model of the power distributionsystem to determine the transfer impedance values as the function offrequency at the one or more specific locations previously chosen 560.In one embodiment, the model is effectuated by running computer programson the computer system. Additional details may be found in thedescription of FIGS. 8-9.

The method then preferably compares the transfer impedance values as thefunction of frequency at the one or more specific locations to thetarget impedance for the power distribution system 565. In oneembodiment, one or more graphs are output which illustrates the transferimpedance values as a function of frequency. Preferably, the graphs arecomputer generated. In another embodiment, the method a resultant noiselevel for the power distribution system due to the current sources andthe decoupling components at the specific locations. In still anotherembodiment, the method outputs the plurality of resultant impedances atthe plurality of specific locations in the power distribution systemdynamically as a function of frequency.

Preferably, the method determines at least a portion of a “bill ofgoods” for the power distribution system based upon the results ofeffectuating the model 570. The bill of goods lists all relevantinformation from the selecting and placing of the various decouplingcomponents. The bill of goods is preferably sufficient to allow massproduction of the electrical interconnecting apparatus modeled to occurwith proper decoupling of the final product. Although the method isshown in flowchart form, it is noted that portions of FIG. 5 may occurconcurrently or in different orders.

FIG. 6—Method for Measuring ESR

FIG. 6 illustrates a flowchart of an embodiment of a method formeasuring the ESR of an electrical device. The method comprisescalibrating an impedance tester 610. Calibrating preferably comprisesconnecting the test heads to the impedance tester prior to all otherwork. In a preferred embodiment, the impedance tester is aHEWLETT-PACKARD model 4291A RF Impedance/Material Analyzer. The testheads preferably comprise a low impedance test head, an APC7 connectorfor the test head, and an adapter to couple APC7 to an SMA connector.Calibrating preferably involves three test cases using a 50Ω load, ashort, and an open circuit.

The method verifies 620 the calibration performed in 610 before mountingthe electrical device. Verification preferably comprises comparing theexpected smith chart reflection coefficient for each test case with theexperimentally determined reflection coefficient. After the impedancetest passes the calibration, the device is securely coupled to theimpedance tester 630. Preferably, securely coupling the device to thetester comprises soldering the device to an SMA connector by connectingone side of the device to the central post and the other side of thedevice to the outer connector. In another embodiment, securely couplingthe device to the tester comprises mounting the device on the tester insuch a fashion that stray capacitances and inductances are mostlyeliminated. The SMA connector is then mounted to the impedance tester.

The method measures the impedance of the device as a function offrequency over the desired frequency range 640. In a preferredembodiment, both the magnitude and the phase angle of the impedance aremeasured. Preferably, the measurement is repeated multiple times and theresults averaged. The method then verifies the results of themeasurements 650. Preferably, verification comprises comparing 180° tothe phase angle shift at the frequency at which the device has a minimummeasured impedance value. If the phase shift at the frequency at whichthe device has a minimum measured impedance value is not 180° at anacceptable uncertainty, then the results are discarded and the methodperformed anew. If the phase shift at the frequency at which the devicehas a minimum measured impedance value is 180° at an accepteduncertainty, then the ESR of the device is the magnitude of theimpedance at the frequency at which the device has a minimum measuredimpedance value is 180°. Although the method is shown in flowchart form,it is noted that portions of FIG. 6 may occur concurrently or indifferent orders.

In a preferred embodiment, measuring the impedance as a function offrequency is comprised as follows. Set the MAG (|Z|) and (θ_(Z)) from“Meas” under the dual parameter key on the HP 4291A. Choose frequencyrange from 1 MHz to 1.8 GHz under the sweep button menu. Choose sweeptype as logarithmic. Choose Marker search under search button and set itto minimum. Set marker search to on. Click on “Bw/Avg” menu undermeasurement block. Choose Sweep average and set average factor to 20.Hit sweep average start button to start taking measurements as afunction of frequency. Note the minimum value after the averagingcounter reaches 20. Repeat steps for each device.

FIG. 7—Method for Selecting and Placing Decoupling Components

FIG. 7 illustrates a flowchart of an embodiment of a method forselecting decoupling components and placing the decoupling components ina power distribution system. The method first determines resonancefrequencies for the electrical interconnection apparatus, the activedevices, and the power supply 710. Note that “resonance frequency”includes the operating frequencies and harmonics of the active devicesand the power supply. Integer fractions of these frequencies may also beconsidered as resonance frequencies. The resonance frequencies of theelectrical interconnection apparatus are also described as boardresonance frequencies or board frequencies. The method then selectsappropriate decoupling components 715. Appropriate decoupling componentshave approximately corresponding resonance frequencies to the systemresonance frequencies determined in 710. The method next places theappropriate decoupling components in the model at appropriate andcorresponding locations for the system resonance frequencies 720. Afterthe model calculations are completed, the appropriate decouplingcomponents will be placed on the electrical interconnection apparatus.

In various embodiments, the electrical interconnection apparatus mayhave one or more board resonance frequencies, with each of the boardresonance frequencies corresponding to one or more particular dimensionsof the electrical interconnection apparatus. Placement of a decouplingcomponent 720 corresponding to a particular board resonance frequency ispreferably at a location corresponding to the particular dimension inquestion.

In one embodiment, the method selects first decoupling componentscorresponding to the board resonance frequencies 715. In anotherembodiment, the method selects second decoupling componentscorresponding to the active device operating frequencies 715. In stillanother embodiment, the method selects third decoupling componentscorresponding to one or more harmonics of the active device operatingfrequencies 715. The method may also select additional decouplingcomponents corresponding to additional board resonance frequencies,active device operating frequencies or harmonics, or interactionresonance frequencies 715.

In an embodiment where the electrical interconnection device hasapproximately a rectangular shape, the first dimension corresponds to aneffective length and the second dimension corresponds to an effectivewidth. The preferred locations for placing decoupling componentscorresponding to the board resonance frequencies for the first andsecond dimensions include the edges along the length and the width. Apreferred location along the dimension includes the midpoint of thedimension.

In one embodiment, selecting appropriate decoupling components withresonance frequencies approximately corresponding to the resonancefrequencies of the power distribution system 715 includes selecting thenumber of each of the decoupling components. The number of each of thedecoupling components is chosen in one embodiment based upon thefrequency range of interest and the impedance profiles of the pluralityof possible decoupling components. In another embodiment, the numbersare chosen by a computer system. The computer system may access adatabase of values on the plurality possible decoupling components,including values for physical and/or electrical characteristics.Electrical characteristics included in the database may include ratedcapacitance, equivalent series resistance, and/or mounted inductance.

In another embodiment, the method for selecting decoupling componentsand placing the decoupling components in the model further compriseseffectuating the model and determining the system impedance response atone or more selected locations. If the system impedance response at theone or more selected locations is above a target impedance, the methodselects additional decoupling components in the proper frequency range.The method places the additional decoupling components in availablelocations. The available locations may be constrained due to existingdevices on the electrical interconnection apparatus, including otherdecoupling components.

In still another embodiment, the method may include comparing animpedance of each particular one of the decoupling components chosen bythe method to the target impedance. The method may further select anumber of each particular one of a decoupling components to provide atotal impedance at or below the target impedance as a part of selectingappropriate decoupling components 715. In yet another embodiment, themethod selects decoupling components above the lowest board resonancefrequency. In another embodiment, the method also selects decouplingcomponents above a highest resonance frequency of the decouplingcomponents. Additional details on selecting particular decouplingcomponents and the number of each particular one of the decouplingcomponents may be found elsewhere in this disclosure. Although themethod is shown in flowchart form, it is noted that portions of FIG. 7may occur concurrently or in different orders.

FIG. 8—Computer System and Method for Selecting Decoupling Components

FIG. 8A illustrates a block diagram of an embodiment of a computersystem for selecting decoupling components. As shown, the computersystem includes a local computer 800 and a remote computer 850 coupledby a networking connection 890. In one embodiment, the local computer800 and the remote computer 850 are unified as a single computer, wherethe networking connection 890 comprises a bus in the single computer.Both the local computer 800 and the remote computer 850 are operable toaccept input from a database of physical and/or electricalcharacteristic data for a plurality of decoupling components 840. Invarious embodiments, the database may be comprised in the local computer800 or in remote computer 850. In a preferred embodiment, the databaseis comprised in remote computer 850 and accessible to the local computer800 through the networking connection 890. In another embodiment, thedatabase 840 is comprised external to both the local computer 800 andthe remote computer 850, such as on a database computer.

As shown, the local computer 800 is operable execute a first program,preferably a web browser 810. The web browser 810 is operable to run aninteractive applet 820, preferably a JAVA applet, and to accept anddisplay graphical output 830. Alternative embodiments may comprise aJavaScript program or HTML code. The JAVA applet 820 outputs componentand placement data using the http POST method to the remote computer.The CGI script 855 receives the component and placement data and eitherincludes or calls a PERL program to build a SPICE deck 860. In otherembodiments, CORBA, remote method invocation (RMI), or other methods maybe used. The SPICE deck output of the PERL program 860 is sent to asimultaneous-equation-solver program, preferably a SPICE simulator suchas HSPICE (available from Avant! Corporation, Fremont, Calif.), whichexecutes the SPICE deck 865. The HSPICE output is preferably convertedby OCTAVE and GNUPlot into a graph 870. The graph from 870 is preferablysent from the remote computer 850 to the local computer 800 to bedisplayed as graphic output 830 in the web browser 810. The actions ofthe CGI script 855 may also be performed by a second program. In oneembodiment, the second program comprises thesimultaneous-equation-solver program. In another embodiment, thesimultaneous equation solver program comprises a circuit-solver program.Other embodiments of the second programs are also contemplated,including custom hardware or software.

FIG. 8B illustrates a flowchart of an embodiment of a method fordetermining decoupling components for a power distribution system,preferably using the computer system of FIG. 8A. Actions 801 (above theline) preferably take place on the local computer 800. Actions 851(below the line) preferably take place on the remote computer 850. Inone embodiment, the actions 801 and 851 all take place in a singlecomputer system. In another embodiment, the actions 801 and 851 takeplace outside the computer system. Systems parameters are defined in806. Preferably, the system parameters include power supply voltage,allowable power supply ripple, total current consumption, power supplypoll frequency, power supply zero frequency, first and second powersupply resistances, physical dimensions of the electricalinterconnection device, dielectric thickness and constant, metalizationthickness of the electrical interconnection device, and the frequencyrange of interest.

The system parameters defined in 806 are used to calculate values forthe target impedance and one or more board resonance frequencies 807.Configuration parameters are defined in 821. The integration parameterspreferably include weighting factors and mounted inductances for theplurality of decoupling components. For purposes of this disclosure,mounted inductance refers to a loop inductance based on the geometry ofthe decoupling components, pad geometry, distance to the power planes,and the location on the power planes. Values are extracted from thedatabase of various physical and/or electrical characteristics for aplurality of decoupling components 841. As shown, the databasepreferably includes the capacitance and ESR for the plurality ofpossible decoupling components.

The calculated values 807, the configuration definitions 821, and thedatabase values 841 are input to calculate the decoupling componentresonance frequencies, and the optimum number of each chosen decouplingcomponent 822. In one embodiment, the optimum number of each chosendecoupling component chosen for given frequency is the ESR of thedecoupling component divided by the target impedance multiplied by theweighting factor. The decoupling component frequencies are preferablycalculated using the equation given above.

Spatial placements for decoupling components, current sources, powersupply, and selected locations or probe points are chosen in 823,preferably by a user. Further details on placing the decouplingcomponents in the model of the power distribution system are givenelsewhere in this disclosure. Spatial placement data 823 and systemparameter definitions 806 are combined into spatial placement data,inductance data, electric interconnection device data, and power supplydata 824 to be sent to the remote computer 850.

The data that were sent to the remote computer 824 are used to build aSPICE deck 861. The SPICE deck is used as input for a SPICE analysis866, preferably using HSPICE. Output from the SPICE analysis 866 isprocessed to create graphical output 871. The graph the output returnedto the local computer 872, preferably to the web browser 810. Thegraphic display is preferably displayed on the local computer 826,preferably as an HTML page in the web browser 810. In one embodiment,the HTML page comprises an SGML page, or other program as desired.Although the method is shown in flowchart form, it is noted thatportions of FIG. 8B may occur concurrently or in different orders.

FIG. 9—Another Embodiment of the Computerized Method

FIG. 9 illustrates a flowchart of an embodiment of a computerized methodfor determining the decoupling components for a power distributionsystem. As shown, the method calculates the target impedance for thepower distribution system 900. The target impedance is preferablycalculated as a power supply voltage times the allowable power supplyripple divided by the total current. In a preferred embodiment, thetotal current is normalized to one ampere. The calculated targetimpedance is used to calculate an optimum number of each availabledecoupling component 905. The optimum number is preferably defined asthe ESR of the decoupling component divided by the target impedancemultiplied by the weighting factor. The method also calculates theresonance frequency of each available decoupling component 910. Theresonance frequency is preferably calculated as the inverse of two pimultiplied by the square root of the product of the mounted inductanceand the capacitance of the decoupling component. The method alsocalculates board resonance frequencies 915, preferably based upon thedimensions of the electrical interconnection device and stackup on theelectrical interconnection device.

The method performs single node analysis to compare the compositeimpedance profile of the electrical interconnection device, includingdecoupling components, to target impedance. In single node analysis,spatial locations are not taken into account, as in the modelillustrated in FIG. 2. The method next compares the results of thesingle node analysis to the target impedance 925 to determine if thecomposite impedance profile of the electrical interconnection device isacceptable. Acceptable is preferably defined as the target compositeimpedance profile being at or below the target impedance. If thecomposite impedance profile of the electrical interconnection device isnot acceptable, the method varies one or more of the input parameters930 and again performs single node analysis 920.

If the composite impedance profile of the electrical interconnectiondevice after single node analysis is acceptable 925, then the methodproceeds to spatially place the decoupling components, the currentsources, the power supply, and the specific probe locations in the model935. The locations chosen for devices placed in the model are preferablyinfluenced by the board resonance frequencies 910 and the capacitorresonance frequencies 915. Additional details on placing decouplingopponents for the power distribution system are given elsewhere in thisdisclosure.

The method next performs multi-node analysis 940. In a preferredembodiment, multi-node analysis corresponds to performing HSPICEanalysis 866. The results of the multi-node analysis are observed 945.If the results are acceptable in 950, the power distribution design isconsidered complete 965. The preferred criteria for accepting theresults of the multi-node analysis are that the system transferimpedance is below the target impedance over the frequency range ofinterest. Should results not be acceptable in 950, method modifies thechoice of the decoupling components, the number of each the decouplingopponents, and/or placement of the decoupling components 960 andreanalyzes the model using multi-node analysis 940. Although the methodis shown in flowchart form, it is noted that portions of FIG. 9 mayoccur concurrently or in different orders.

Numerous variations and modifications will become apparent to thoseskilled in the art once the above disclosure is fully appreciated. It isintended that the following claims be interpreted to embrace all suchvariations and modifications.

What is claimed is:
 1. A method for decoupling a power distributionsystem, the method comprising: creating a model of an electronic circuitincluding said power distribution system, wherein said model includes aplurality of cells interconnected at predetermined nodes, wherein eachof the cells represents an electrical characteristic of said electroniccircuit, and wherein said power distribution system includes a powersupply, and wherein said model of electronic circuit includes attributesof said power supply, wherein said power supply is characterized in saidmodel by one or more pole frequencies, one or more zero frequencies, andone or more resistances; selecting one or more decoupling capacitors forsaid electronic circuit, and updating said model of said electroniccircuit to include electrical characteristics of said decouplingcapacitors; simulating operation of said electronic circuit using saidmodel of electronic circuit; determining a transfer impedance value ateach of nodes corresponding to one or more specific locations in saidelectronic circuit; comparing said transfer impedance value at each ofsaid one or more nodes to a target impedance; repeating said selecting,said simulating, said determining, and said comparing until saidtransfer impedance value at each of said one or more nodes is at orbelow said target impedance, and providing an output that specifieselectrical characteristics of specific decoupling capacitors at specificnodes that results in the transfer impedance value at said each nodecorresponding to one or more specific locations to be at or below thetarget impedance.
 2. The method as recited in claim 1, wherein saidplurality of cells is arranged in an M×N grid.
 3. The method as recitedin claim 2, wherein M and N are of equal value.
 4. The method as recitedin claim 1, wherein said power distribution system includes a printedcircuit board having a power plane and a ground plane, and wherein theelectrical characteristic represented by each cell of said modelincludes attributes of said printed circuit board.
 5. The method asrecited in claim 1, wherein each of said cells is modeled by electricalcharacteristics corresponding to one or more transmission lines and oneor more resistors.
 6. The method as recited in claim 5, wherein each ofsaid transmission lines is characterized by at least one impedance valueand at least one time delay value, and wherein said impedance value andsaid time delay value are based on physical dimensions of said powerdistribution system.
 7. The method as recited in claim 1, wherein saidone or more decoupling capacitors are selected from a database ofdecoupling capacitors.
 8. The method as recited in claim 7, wherein saiddecoupling capacitors are selected based on one or more of the followingcharacteristics: a capacitance value; a mounted inductance value; and anequivalent series resistance value.
 9. The method as recited in claim 8,wherein a specific quantity of decoupling capacitors for the powerdistribution system at a given frequency is determined based on aformula Q=ESR/Z_(T), wherein ESR is the equivalent series resistance ofa selected decoupling capacitor for said given frequency, Z_(T) is thetarget impedance, and Q is the quotient obtained from said formula. 10.The method as recited in claim 9, wherein said specific quantity isdetermined by rounding said quotient up to the nearest integer value.11. The method as recited in claim 1, wherein said target impedance isselected based on one or more of the following: power supply voltage;total current consumption by said electronic circuit; and allowablevoltage ripple.
 12. The method as recited in claim 1, wherein saidelectronic circuit includes one or more active components, and whereinsaid active components are characterized in said model of electroniccircuit as current sources and/or current sinks.
 13. The method asrecited in claim 1, wherein said active components include one or moreof the following: processors, memories, application specific integratedcircuits (ASICs), or logic IC's.
 14. The method as recited in claim 1,wherein said model of said electronic circuit is a mathematical model.15. The method as recited in claim 14, wherein said model of saidelectronic circuit is a SPICE model.
 16. The method as recited in claim1 further comprising determining a physical location within saidelectronic circuit for each of said one or more decoupling capacitors,wherein said physical location is represented within said model of saidelectronic circuit by one of said predetermined nodes.
 17. A system fordetermining decoupling for an electronic circuit, the system comprising:a computer system configured to: accept inputs for creating a model ofsaid electronic circuit including a power distribution system, whereinsaid power distribution system includes a power supply, and wherein saidmodel of electronic circuit includes attributes of said power supply,wherein said power supply is characterized in said model by one or morepole frequencies, one or more zero frequencies, and one or moreresistances, wherein said model includes a plurality of cellsinterconnected at predetermined nodes, wherein each of the cellsrepresents an electrical characteristic of said electronic circuit;select one or more decoupling capacitors for said electronic circuit,and updating said model to include electrical characteristics of saiddecoupling capacitors; simulate operation of said electronic circuitusing said model of electronic circuit; determine a transfer impedancevalue at each of one or more nodes corresponding to specific locationsin said electronic circuit; compare said transfer impedance value ateach of said one or more nodes to a predetermined target impedance;repeat said selecting, said simulating, said determining, and saidcomparing until each of said transfer impedance values is at or belowsaid target impedance; and provide an output that specifies electricalcharacteristics of specific decoupling capacitors at specific nodes thatresults in the transfer impedance value at said each node correspondingto one or more specific locations to be at or below the targetimpedance.
 18. The system as recited in claim 17, wherein said pluralityof cells is arranged in an M×N grid.
 19. The system as recited in claim18, wherein M and N are of equal value.
 20. The system as recited inclaim 17, wherein said power distribution system includes a printedcircuit board having a power plane and a ground plane, and wherein theelectrical characteristic represented by each cell of said modelincludes attributes of said printed circuit board.
 21. The system asrecited in claim 17, wherein each of said cells is modeled by electricalcharacteristics corresponding to one or more transmission lines and oneor more resistors.
 22. The system as recited in claim 21, wherein eachof said transmission lines is characterized by at least one impedancevalue and at least one time delay value, and wherein said impedancevalue and said time delay value are based on physical dimensions of saidpower distribution system.
 23. The system as recited in claim 17,wherein said one or more decoupling capacitors are selected from adatabase of decoupling capacitors.
 24. The system as recited in claim23, wherein said one or more decoupling capacitors are selected based onone or more of the following: a capacitance value; a mounted inductancevalue; and an equivalent series resistance value.
 25. The method asrecited in claim 24, wherein a specific quantity of decouplingcapacitors for the power distribution system at a given frequency isdetermined based on a formula Q=ESR/Z_(T), wherein ESR is the equivalentseries resistance of a selected decoupling capacitor for said givenfrequency, Z_(T) is the target impedance, and Q is the quotient obtainedfrom said formula.
 26. The system as recited in claim 25, wherein saidspecific quantity is determined by rounding said quotient up to thenearest integer value.
 27. The system as recited in claim 17, whereinsaid target impedance is selected based on one or more of the following:power supply voltage; total current consumption by said electroniccircuit; and allowable voltage ripple.
 28. The system as recited inclaim 17, wherein said electronic circuit includes one or more activecomponents, and wherein said active components are characterized in saidmodel of electronic circuit as current sources and/or current sinks. 29.The system as recited in claim 28, wherein said active componentsinclude one or more of the following: processors, memories, applicationspecific integrated circuits (ASICs), or logic IC's.
 30. The system asrecited in claim 17, wherein said model of said electronic circuit is amathematical model.
 31. The system as recited in claim 30, wherein saidmodel of said electronic is a SPICE model.
 32. The system as recited inclaim 17, wherein said system is further configured to determine aphysical location within said electronic circuit for each of said one ormore decoupling capacitors, wherein said physical location isrepresented within said model of said electronic circuit by one of saidpredetermined nodes.